Implantable stimulation devices deliver electrical stimuli to nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability with any implantable medical device or in any implantable medical device system.
An SCS system typically includes an Implantable Pulse Generator (IPG), whose structure and construction is further described in U.S. Provisional Patent Application No. 61/874,194, entitled “Construction for an Implantable Medical Device Employing an Internal Support Structure,” filed Sep. 5, 2013 (“the '194 Application”), which is incorporated herein by reference in its entirety. The IPG 10 of the '194 Application is shown in FIG. 1, which includes a biocompatible device case 30 that holds the circuitry and battery 34 (FIG. 2) necessary for the IPG to function. The IPG 10 is coupled to electrodes 16 via one or more electrode leads 14 that form an electrode array 12. The electrodes 16 are carried on a flexible body 18, which also houses the individual signal wires 20 coupled to each electrode 16. The signal wires 20 are also coupled to proximal contacts 22, which are insertable into a lead connector assembly 50 fixed in a header 28 on the IPG 10, which header can comprise an epoxy for example. Once inserted, the proximal contacts 22 connect to header contacts 58 in the lead connector assembly 50, which header contacts 58 are in turn coupled by feedthrough pins 48 (not shown) to circuitry within the case 30, as will be explained subsequently. In the illustrated embodiment, there are sixteen electrodes 16 (E1-E16) split between two leads 14, although the number of leads and electrodes is application specific and therefore can vary. In a SCS application, electrode leads 14 are typically implanted on the right and left side of the dura within the patient's spinal cord. The proximal contacts 22 of the leads 14 are then tunneled through the patient's tissue to a distant location, such as the buttocks, where the IPG case 30 is implanted, at which point they are coupled to the lead connector assembly 50 in the header 28.
FIG. 2 shows perspective bottom and top sides of the IPG 10 with the case 30 removed so that internal components can be seen. In particular, a battery 34, communication coil 40, and a printed circuit board (PCB) 42, can be seen. As explained in the '194 Application, these components are affixed to and integrated using a rigid (e.g., plastic) support structure 38. Battery 34 in this example is a permanent, non-wirelessly-rechargeable battery. (Battery 34 could also be rechargeable, in which case either coil 40 or another recharging coil would be used to wirelessly receive a charging field that is rectified to charge the battery 34). The communication coil 40 enables communication between the IPG 10 and a device external to the patient (not shown), thus allowing bidirectional communication to occur by magnetic induction.
The ends of coil 40 are soldered to coil pins 44 molded into the support structure 38 to facilitate the coil 40's eventual connection to circuitry on the IPG PCB 42. IPG PCB 42 integrates the various circuits and electronics needed for operation of the IPG 10. As shown in FIG. 2, coil 40 is proximate to the bottom side of the support structure 38 and case 30, while the IPG PCB 42 is proximate to the top side.
Construction of the lead connector assembly 50 is shown starting with FIG. 3A. Construction begins with an elastomer connector seal 52 formed of silicone for example. As can be seen, the connector seal 52 has been molded to include contact recesses 54 separated by narrower-diameter separator portions 55 formed of the connector seal 52 material. The contact recesses 54 are accessible through slits 56 in the side of the connector seal 52. During construction, header contacts 58, which are largely donut-shaped and formed of a rigid conductive material, are pressed through the slits 56, and come to rest inside of the seal 52 in the contact recesses 54. Once inserted, the header contacts 58 are captured firmly, and are electrically isolated from each other by the separator portions 55 of the connector seal 52. In the example shown, the connector seal 52 includes eight header contacts 58, which eventually will couple to the eight proximal contacts 22 on one of the leads 14 (FIG. 1).
Once all header contacts 58 have been positioned in the seal 52, adhesive is applied to opening 62 at one end of the seal 52, and a connector block 66 is inserted into the opening 62 and adhered to the connector seal 52. A medical grade adhesive suitable for this task includes Silastic® medical adhesive manufactured by Dow Corning Corporation or other adhesives provided by NuSil Silicone Technology LLC. Curing of such adhesives can take up to 12 hours. A platinum end cap 68 is also inserted into the opening 64 at the other end of the seal 52. After inserting the end cap 68 and adhesive curing of the connector block 66 to the seal 52, the resulting connector seal subassembly 70 is shown in FIG. 3B.
Continuing with FIG. 3B, connector seal subassembly 70 is then affixed within a recess 74 in a carrier 72, which may be formed of a rigid plastic such as polyurethane. As shown, the carrier 72 can accompany two connector seal subassemblies 70 on both of its sides to support an IPG 10 with sixteen electrodes 16 in this example. The connector seal subassembly(ies) 70 can be affixed and cured within the carrier 72 using an adhesive such as those just mentioned. Adhesive can be applied to the areas of the carrier that will be adjacent to the connector block 66 and the end cap 68 to ensure a secure placement. The resulting carrier subassembly 80 is shown in FIG. 3C.
After the carrier subassembly 80 has been completed, it is mechanically and electrically connected to a feedthrough 32 and feedthrough pins 48 to complete the lead connector assembly 50, as shown in FIG. 3D. To do this first, feedthrough pins 48 are slipped through the feedthrough 32, and then insulation tubes (not shown) are put on each of the feedthrough pins 48 to cover a portion of the feedthrough pins 48 between the feedthrough 32 and the slits 56. The insulation tubes are shorter than the feedthrough pins 48, thus allowing some portion of first ends of each feedthrough pin 48 to remain exposed for connection to the contacts 58. Adhesive is then placed on each feedthrough pin 48 to adhere the insulation tubes to the pins, and then the uncovered first ends of the pins 48 are soldered to the header contacts 58 through the slits 56 in the connector seal 52. After soldering, the silts 56 containing the soldered connections are then covered with adhesive and cured as before to create a hermetic seal.
The now completed lead connector assembly 50 can then be coupled to the remainder of the IPG circuitry, as discussed in detail in the above-incorporated '194 Application. Such remaining IPG construction steps are not discussed here in detail, but involve soldering the second ends of the feedthrough pins 48 to the PCB 42; affixing the IPG circuitry in the case 30; welding the case 30 together and to the feedthrough 32; and molding the header 28 over the lead connector assembly 50 and to the case 30.
The inventors see that this process for forming the lead connector assembly 50 for the IPG 10 can be improved upon. For one, the process at several places requires the use of adhesive: to adhere the connector block 66 and end cap 68 to the connector seal 52 (FIG. 3B); to affix the connector seal subassembly 70 inside of the carrier 72 (FIG. 3C); to seal the insulation tubes to the feedthrough pins 48; and to cover the slits 56 in the connector seal 52 once the header contacts 58 have been soldered to the feedthrough pins 48 (FIG. 3D). This slows down manufacture of the lead connector assembly 50, in particular because the adhesive must be cured at each stage before subsequent construction steps can begin. Additionally, certain of the components, such as the end cap 68, are costly.
Moreover, there is no good means for testing the lead connector assembly 50, or its constituent subassembly(ies) 70 or 80, with respect to hermeticity—i.e., with respect to how effectively their construction has rendered them impervious to moisture and/or epoxy ingress.
This is unfortunate, as it means that assembly 50 or subassembly 70 or 80 could have a hermeticity concern that would not be noticeable during IPG manufacturing. This wastes manufacturing resources, as a defective lead connector assembly 50 may be coupled to otherwise functioning IPG circuitry, and worse can affect IPG reliability after implantation into a patient. An improved lead connector assembly remedying these concerns is thus sought, and is disclosed by the inventors.